Proton-induced displacement damage in ZnO thin film transistors: Impact of damage location

We have investigated the displacement damage (DD) effect on the electrical characteristics of ZnO thin film transistors (TFTs) based on its location of origin in the device structure. The area subjected to the maximum proton dose induces a maximum DD effect in that particular location. ZnO TFTs with two different passivation layer thicknesses were prepared to obtain maximum proton dose distribution in either the ZnO channel layer or ZnO/SiO2 interface. The devices were irradiated by a proton beam with an energy 200 keV and 1 × 1014 protons/cm2 fluence. Transport of Ions in Matter (TRIM) simulation, followed by calculation of depth distribution of the nonionizing energy loss (NIEL), illustrated different proton dose distribution profiles and NIEL profiles along the depth of the device for these two types of samples. The sample with the maximum proton dose peaks at the ZnO/SiO2 interface exhibited a significant degradation in device electrical characteristics as compared to the negligible degradation of the sample when the maximum proton dose was absorbed in the ZnO layer. Therefore, the investigation into the radiation hardness of proton-irradiated ZnO TFTs is non-trivial since the displacement damage induces drastic changes on the device characteristics based on the damage location.